The primary research goal of this Pathway to Independence proposal is to dissect and characterize intrinsic and innate barriers to respiratory virus infections. Although respiratory viruses pose a major health burden, there is a paucity of effective, available antiviral strategies. Understanding the mechanisms by which individual host factors inhibit these viral infections may lead to new antiviral strategies. The recent discovery o several interferon-stimulated genes (ISGs) that inhibit viruses at late stages of their infectious cycles (viperin - budding; tetherin - detachment; plasminogen activator inhibitor 1 - maturation) validated such stages as attractive antiviral targets. In the mentored phase of this K99 award, the candidate will be trained in next-generation transcriptome profiling and bioinformatics to identify the late-acting antiviral program raised by ELF1, an ISG and transcription factor conferring broad antiviral resistance. In addition, based on her previous identification of late-acting inhibitors of influenza A virus, she will screen for antiviral ISG activity against a panel f other respiratory viruses, consisting of influenza B virus, human parainfluenzavirus, respiratory syncytial virus, human metapneumovirus, human rhinovirus and human adenovirus. Finally, the candidate will receive training on CRISPR/Cas9-mediated genome editing of embryonic stem cells (ESCs), and establish protocols to differentiate polarized human airway epithelium cultures from lung progenitor cells. These cultures will serve to validate findings from conventional tissue culture in a more physiologically relevant model system. Additional components of the candidate's comprehensive career development plan are courses and seminars in ethics and grant writing. The training phase will be carried out in the laboratory of Dr. Charles Rice at The Rockefeller University (RU), one of the world's leading laboratories in virology research. In addition to the significant resources and basic science expertise in this lab, the candidate will also benefit from RU's vibrant research community. A critical component of career development will be the close counsel of a highly experienced Advisory Committee, composed of Dr. Charles Rice, Dr. Jean-Laurent Casanova (both RU), and Dr. Adolfo Garcia-Sastre (Mt Sinai School of Medicine). The innovative skills and meaningful data sets obtained in the K99 training phase will set the stage for detailed mechanistic studies on ELF1 and other selected hits in the independent phase, and will be key to succeed as a young independent investigator in this highly competitive field of research. In all, the training will fulfill both the candidate's short-erm goals of adding new technologies, skills, and experience to her portfolio, and her long-term goals, to become an independent investigator with a research focus on the virus-host interplay in the context of the innate immune system.